This invention is directed to a heavy-duty pump jack of the type used in oil well pumping. The pump jack eliminates the usual gear box by employing belt-driven speed reduction and leverage for force multiplication.
The modern oilfield pump jack employs a prime mover such as an electric motor or internal combustion engine as its primary power source. The rotary prime mover is connected to a gear box with an output crank. The gear box reduces the speed and multiplies the torque so that the crank can be coupled through a connecting rod directly to the walking beam. The walking beam carries a horse head from which the pump string depends. Counter weights are applied to the walking beam and/or the crank to attempt to equalize the load on the prime mover.
The modern demand for pumping units has outstripped the supply of gear boxes. As a result, there are wells which could usefully employ a pump jack, but gearboxes are not available for pump jacks for those wells. Consequently, there is need for oil well pump jacks which do not employ a gear box.